1. Field of the Invention
This invention relates to a wireless communication system and components thereof. In particular, this invention is concerned with controlling the measuring of the quality of wireless links. Such measurements are commonly a significant factor in determining whether or not a handover procedure should be performed.
2. Description of the Related Art
In order to determine whether or not a handover procedure is to be performed, handover-related measurements are performed for neighbouring cells. Some of these measurements cannot be performed by a User Equipment (UE), e.g. a cellular phone, while the UE is also listening for data or transmitting data. Accordingly, in order to allow the UE to perform such measurements gaps in the transmission and reception of data are scheduled.
The original Universal Mobile Telecommunications System (UMTS) Wideband Code Division Multiple Access (WCDMA) standard specifies a static mechanism for scheduling the transmission/reception gaps in which the UE sends information to the Universal Terrestrial Radio Access Network (UTRAN) indicating whether transmission/reception gaps are required for various different types of measurement. The UTRAN then configures transmission/reception gaps in accordance with the received information, and sends a measurement control message to the UE indicating the gap configuration.
While the UMTS static mechanism is straightforward, the UMTS static mechanism lacks flexibility and does not fully take into account the differing measurement capabilities of different UE.
Another feature of the original UMTS WCDMA standard is power-saving connected mode states in which discontinuous reception/transmission (DRX/DTX) between the UE and the UTRAN occurs. In the power-saving connected mode states the UE controls handovers, i.e. the UE performs cell re-selection. In order to maximize the power saving by the UE handover-related measurements are performed in accordance with the DRX/DTX period.
Further, the UTRAN may transmit one or more ‘Ssearch’ parameters which are used by the UE to determine the frequency at which handover-related measurements are performed. In particular, the UE is only required to perform a measurement if the link quality of the existing link is below the Ssearch parameter for that measurement. Separate Ssearch parameters are defined for intra-frequency, inter frequency and inter-Radio Access Technology (RAT) measurements both for the case where Hierarchical Cell Structure (HCS) is employed and the case where HCS is not employed.
An Evolved Universal Terrestrial Radio Access (E-UTRA) scheme is presently being specified by the 3rd Generation Partnership Project (3GPP). Some details of E-UTRA have already been agreed, see for example specification 3GPP TS 36.300 “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2”, Release 8. In particular, it has been agreed that in a Radio Resource Control (RRC) connected mode:                the E-UTRAN sends dedicated messages to control the measurements to be performed by the User Equipment (UE);        measurements for which the UE requires transmission and/or reception gaps are classified as ‘gap assisted’;        measurement gaps are provided and controlled by the E-UTRAN, i.e. the UE cannot autonomously change the configuration of the gaps;        a discontinuous communication mode can be configured at Radio Link Control/Medium Access Control (RLC/MAC) level for UE power saving and efficient resource utilization; and        the E-UTRAN controls the measurements to be performed by a UE.        
It has been proposed that the UE provides further assistance in the gap configuration process. The motivation for this proposal is to take better account of the differing measurement capabilities of different UEs.